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Diffstat (limited to 'Documentation/arm64/booting.txt')
| -rw-r--r-- | Documentation/arm64/booting.txt | 43 |
1 files changed, 35 insertions, 8 deletions
diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt index 37fc4f632176..85af34d55cee 100644 --- a/Documentation/arm64/booting.txt +++ b/Documentation/arm64/booting.txt @@ -72,27 +72,54 @@ The decompressed kernel image contains a 64-byte header as follows: u32 code0; /* Executable code */ u32 code1; /* Executable code */ - u64 text_offset; /* Image load offset */ - u64 res0 = 0; /* reserved */ - u64 res1 = 0; /* reserved */ + u64 text_offset; /* Image load offset, little endian */ + u64 image_size; /* Effective Image size, little endian */ + u64 flags; /* kernel flags, little endian */ u64 res2 = 0; /* reserved */ u64 res3 = 0; /* reserved */ u64 res4 = 0; /* reserved */ u32 magic = 0x644d5241; /* Magic number, little endian, "ARM\x64" */ - u32 res5 = 0; /* reserved */ + u32 res5; /* reserved (used for PE COFF offset) */ Header notes: +- As of v3.17, all fields are little endian unless stated otherwise. + - code0/code1 are responsible for branching to stext. + - when booting through EFI, code0/code1 are initially skipped. res5 is an offset to the PE header and the PE header has the EFI - entry point (efi_stub_entry). When the stub has done its work, it + entry point (efi_stub_entry). When the stub has done its work, it jumps to code0 to resume the normal boot process. -The image must be placed at the specified offset (currently 0x80000) -from the start of the system RAM and called there. The start of the -system RAM must be aligned to 2MB. +- Prior to v3.17, the endianness of text_offset was not specified. In + these cases image_size is zero and text_offset is 0x80000 in the + endianness of the kernel. Where image_size is non-zero image_size is + little-endian and must be respected. Where image_size is zero, + text_offset can be assumed to be 0x80000. + +- The flags field (introduced in v3.17) is a little-endian 64-bit field + composed as follows: + Bit 0: Kernel endianness. 1 if BE, 0 if LE. + Bits 1-63: Reserved. + +- When image_size is zero, a bootloader should attempt to keep as much + memory as possible free for use by the kernel immediately after the + end of the kernel image. The amount of space required will vary + depending on selected features, and is effectively unbound. + +The Image must be placed text_offset bytes from a 2MB aligned base +address near the start of usable system RAM and called there. Memory +below that base address is currently unusable by Linux, and therefore it +is strongly recommended that this location is the start of system RAM. +At least image_size bytes from the start of the image must be free for +use by the kernel. + +Any memory described to the kernel (even that below the 2MB aligned base +address) which is not marked as reserved from the kernel e.g. with a +memreserve region in the device tree) will be considered as available to +the kernel. Before jumping into the kernel, the following conditions must be met: |